Fix pre-existing issues and update README for v2.0

- Fix _infer_state_from_artifacts: SPEC-only maps to research (was bug_find)
- Fix cmd_validate_folder: corrupted .state files now error instead of silent fallback
- Fix upgrade.sh: remove || true, add python3 check, use git rev-parse --git-dir
- Update README.md with --project flag, --can-edit modes, --upgrade, enforcement layers
- Add 6 new tests for inference and validation fixes
- Complete hook-install-process and readme-upgrade-docs tasks

tasks/readme-upgrade-docs/VERDICT.md

@@ -0,0 +1,16 @@
+# Verdict: readme-upgrade-docs
+
+## Status: PASS
+**Completion Date**: 2026-06-15
+
+## Summary
+Updated README.md with comprehensive v2.0 documentation: `--project` flag on all commands, `--can-edit` modes, `--upgrade` for untracked tasks, three enforcement layers, full upgrade process for existing projects, pre-commit hook installation, and updated Key Components.
+
+## Findings
+- All 6 acceptance criteria met
+- 200 tests pass
+- Documentation-only change, no code bugs possible
+- Pre-existing issues in upgrade.sh noted but not in scope
+
+## Score
++10